Technical Field
This application relates to mobile telecommunications systems in general, and in particular relates to a method and apparatus in mobile telecommunications system for user equipment handling of network congestion.
Description of the Related Art
In a typical wireless cellular radio system, user equipment (UE), or a ‘device’, communicates via one or more radio access networks (RANs) to one or more core networks. User equipment (UE) comprises various types of equipment such as mobile telephones (also known as cellular or cell phones, including smart phones), laptops with wireless communication capability, personal digital assistants (PDAs) etc. These may be portable, hand held, pocket sized, installed in a vehicle etc and communicate voice and/or data signals with the radio access network.
In the following, reference may be made to E-UTRAN (e.g. LTE), UTRAN (e.g. UMTS) and GERAN and to particular Standards. However it should be understood that the invention is not intended to be limited to any particular mobile telecommunications system.
A radio access network covers a geographical area typically having a plurality of cell areas. Each cell area is served by at least one base station, which in UMTS and LTE may be referred to as a Node B and enhanced-Node B (eNB) respectively. The base stations communicate at radio frequencies over an air interface with the UEs within range of the base station. Several base stations may be connected to a radio network controller (RNC) in UTRAN systems which controls various activities of the base stations. The radio network controllers are typically connected to a core network.
Various standardization bodies are known to publish specifications/standards and set standards for mobile telecommunication systems. For instance, the 3GPP (Third Generation Partnership Project) has been known to publish and set standards for mobile telecommunications. Within the scope of a particular standardization body, specific partners publish and set standards in their respective areas.
Problems may arise when a UE attempts to communicate with a cell. In UMTS/WCDMA networks for example, UE connection attempts can be rejected by the network due to congestion including equipment failure etc. The congestion may be at the cell, at radio network controller (RNC) or at the entire network, for example. The congestion rejection rate may be worse in densely populated areas, or at certain/busy times of day for a given location. In such cases, if a UE wants to establish a connection from IDLE state, UTRAN typically uses rrcConnectionReject message to reject some of the UEs requesting radio resources through rrcConnectionRequest message transmission. Thus in some aspects, congestion can be defined by receipt of a rejection to a connect request, or failure to receive a response to a connection establishment message, for example. UTRAN vendors typically use a wait time information element (IE) to delay connection attempts of idle mode devices for a specified time. Networks can perform similar throttling of some connected mode UEs (UEs in CELL_PCH (excluding Enhanced Cell FACH capable UEs with a dedicated H-RNTI) and URA_PCH states by specifying a wait time in a cellUpdateConfirm message when a connected mode device initiates a cellUpdate message to request radio link resources.
During this wait time, UE's can wait in real or pseudo CELL_FACH state consuming considerable amounts of battery power. As an example, a typical UMTS UE consumes 3.5 mA during IDLE mode operation (when DRX is set to 7 which is a typically value configured by the network), whereas in CELL_FACH state the current consumption rises to 110 mA. Also, UEs' initiating the radio connection and waiting in pseudo CELL_FACH state are not reachable for paging to initiate mobile-terminated calls in this state, since neither paging control channel (PCCH) (paging TYPE1) applicable for IDLE mode, CELL_PCH and URA_PCH RRC states nor a dedicated control channel (DCCH) applicable for CELL_FACH and CELL_DCH RRC states (paging TYPE2) can reach the UEs.
Such a scenario can also occur if idle mode the UE's connection attempt is implicitly rejected by the network sending no message in response to UE's rrcConnectionRequest message (i.e. a missing rrcConnectionSetup or rrcConnectionReject message on the downlink). In this case, the UE in IDLE mode will re-try connection establishment attempt according to T-300 and N-300 setting in system information block (SIB)1.
UEs in CELL_PCH or URA_PCH states can experience a similar problem when a cellUpdate message is not acknowledged by the network via a cellUpdateConfirm message. In this scenario cellUpdate message is re-transmitted according to T-302 and N-302 setting in the network (SIB1).
For instance, consider a UE that complies with the 3GPP specifications, for instance the UMTS/UTRAN and/or LTE/E-UTRAN protocols. The 3GPP technical specification 25.331, referred to herein as TS 25.331, for example, release 10, addresses the subject of UMTS RRC (Radio Resource Control) protocol requirements between the Radio Access Network (UTRAN) and the UE.
Section 8.1.3.9 of 3GPP TS 25.331 v.10.3.0 states as follows:
“if the IE “wait time” <> ‘0’, wait at least the time stated in the IE “wait time”.
Thus, there is no explicit indication from the 3GPP specification “Standard” of an RRC state for a UE to wait in.
Additionally, UEs are required to go through rrcConnectionRequest transmission to conclude that the network is congested (by reception of an rrcConnectionReject message). This is battery and signalling intensive causing extra strain on already congested network and limited battery capacity of the mobile device.
There are thus proposed strategies for a method and apparatus in mobile telecommunications system for user equipment to handle congestion scenarios efficiently. A number of such strategies are detailed below.
Other aspects and features of the proposed strategy will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of an apparatus and method in mobile telecommunications system user equipment.